I have generated a an ED25519 SSH key pair using
ssh-keygen -t ed25519
The output of the id_ed25519 file is in OpenSSH format:
-----BEGIN OPENSSH PRIVATE KEY-----
...
-----END OPENSSH PRIVATE KEY-----
I would like to convert it to a PEM file format. If it were an RSA key pair, there would be no need for that as an RSA id_rsa key is already in a PEM file format but the ED25519 key pair is an OpenSSH format.
How can I convert this to a PEM file format?
Use
ssh-keygen -p -f path/to/your/key -m pem
to convert your key file to PEM, but be sure to make a backup of the file first.
Taking from https://github.com/pickware/github-action-ssh-agent
I think this would work:
openssl pkey -in ed25519.pem -out ed25519.pub -pubout
It does for a private key generated this way:
openssl genpkey -algorithm ed25519 > ed25519.pem
I haven't tested ssh-keygen's private key format explicitly but I would assume that it is using OpenSSL under the hood. If the private key's base64 starts with "MC", then I would say it probably would be compatible.